The present invention concerns lubricating compositions and more particularly lubricating grease compositions having improved extreme pressure and other beneficial properties.
Many lubricants which are satisfactory under ordinary lubricating conditions do not provide adequate lubrication under the high frictional forces and temperatures that characterize extreme pressure conditions. Under these conditions friction gives rise to localized high temperatures at the metal surfaces. If this situation is not controlled, the metal parts in contact will seize or be scored causing failure of the parts.
Lubricating additives known as extreme pressure agents are employed to increase the load-carrying capacity of lubricants. The extreme pressure agents promote the formation of an antiweld film and thereby prevent welding of the contacting surfaces.
It is known in the art that certain sulfur containing compounds possess extreme pressure properties. However, many impart to the grease composition the undesirable properties of corrosion and staining of the metal surfaces in contact with the composition. Still others do not possess sufficient efficacy. The latter include polymers of 1,3,4-thiadiazole-2,5-dithiol which possess relatively low extreme pressure properties, insufficient for heavy duty applications when used as a sole extreme pressure agent as indicated in U.S. Pat. No. 4,308,182 granted Eckard et al Dec. 29, 1981.
Surprisingly, it has now been discovered that the dimer of 1,3,4-thiadiazole-2,5-dithiol imparts to lubricating grease composition good load carrying ability without causing the composition to corrode or discolor the metal surface to be protected.